Many biochemical tests formerly performed in the laboratory using advanced equipment and skilled labor, can today be performed by a physician, a nurse or even the patient himself/herself, using small, often disposable devices. This is one result of a better understanding of biochemistry and medicine, as well as the ongoing miniaturization of both mechanics and electronics, taking place over the recent decades.
Such tests can be divided into two groups: “one-step tests” where a reaction takes place on a substrate after the addition of sample, and the result is detected as a change of one or more properties of said substrate; and “two-step tests”, where the sample is followed by the addition of a detection conjugate, leading to a specific reaction resulting in a detectable signal.
In most assays, the detection conjugate and possible other reagents is pre-dispensed or integrated in the device, setting aside the need for separate addition of reagents by the user.
The most common type of disposable assay device consists of a zone or area for receiving the sample, a reaction zone, and optionally a transport or incubation zone connecting the receiving and reaction zone, respectively. These assay devices are known as immunochromatography assay devices or simply referred to as strip tests. They employ a porous material, such as nitrocellulose, defining a fluid passage capable of supporting capillary flow. The sample-receiving zone frequently consists of a more porous material, capable of absorbing the sample, and, when the separation of blood cells is desired, effective to trap the red blood cells. Examples of such materials are fibrous materials, such as paper, fleece, gel or tissue, comprised e.g. of cellulose, nitrocellulose, wool, glass fibre, asbestos, synthetic fibers, polymers, etc. or mixtures of the same. The transport or incubation zone commonly consists of the same or similar materials, often with different porosity than that of the sample-receiving zone. Likewise, the reaction zone, which may be integrated with the incubation zone, or constituting the most distal part thereof, commonly consists of similar, absorbing fibrous materials, such as nitrocellulose, or any of the above listed materials.
In an assay device or strip test, the porous material/-s is/are assembled on a carrier, such as a strip of thermoplastic material, paper, cardboard or the like. Further, a cover can be provided, said cover having at least one aperture for receiving the sample, and an aperture or a transparent area for reading the result of the assay.
Nitrocellulose materials are also frequently used as the matrix constituting the transport or reaction zone, connecting the receiving zone and the reaction zone. A significant disadvantage with nitrocellulose is its high non-specific binding of proteins and other bio-molecules. Present test strips however often handle a surplus of sample, reducing the influence of this binding. Another disadvantage of nitrocellulose is its variable quality, both with regard to chemical and physical properties. It is in any case desirable to minimize the sample volume, in line with the tendency to miniaturize the entire test, including minimizing the amounts of reagents, without compromising accuracy and reliability.
WO01/27627 is representative for the technical background, disclosing an assay device for quantification or detection of the presence or absence of an analyte in a liquid sample, comprising a molding permanently or removably attached to a substantially planar plate such that a part of said molding forms a capillary chamber between said plate and the said molding, the device further comprising a chamber into which a test sample and/or reagent can be introduced and further comprising a chamber capable of accommodating an absorbing pad, wherein the said chamber into which a test sample and said chamber capable of holding an absorbing pad are in lateral flow contact via the said capillary chamber.
U.S. Pat. No. 6,436,722 describes a device and method for integrated diagnostics with multiple independent fluid passages, and an absorbing block providing sufficient capillarity to pull the reagents into said absorbing and sustaining a separate second fluid passage that flows in a second direction from a first fluid passage. Notably, the absorbing block is stated to be capable of accommodating a volume of liquid in excess of the total sample volume and the total volume of all other liquid reagents.
The aim of the present inventors was to find alternative constructions, offering ease of production and cost savings, as well as the technical benefits associated with the micropillar structure, disclosed in WO 03/103835, by the same applicant. Further aims, solutions as well as their advantages will be evident to a skilled person upon study of the following description and non-limiting examples.